Bifocal-lens blank



Feb. 5, 1924. 1,482,951

H. J. STEAD BIFOCAL LENS BLANK Filed April 16, 1923 \NV To, '162 Patented at. s, 1924.

PATENT FFlE.

HAROLD J. STE-AD, OF GENEVA, NEW YORK.

mrocannnus BLANK.

' Application filed April 16, 1928. Serial No. 632,839.

To all whom it may concern:

Be itknown that I, HAROLD J. STEAD, a citizen of the United States of America, of Geneva, in the county of Ontario, in the a State of New York, have invented newand useful Improvements in Bifocal-Lens Blanks, of which the following, taken in connection with the accompanying drawings, is a full, clear, and exact description.

This invention relates to a new and improved bifocal lens blank.

' The present practice in producing blanks used for one piece bifocal lenses is to mold both sides of the blank with the same curve, that is, one side concave and the other side convex. Generally, blanks of circular outline have been used from which two or more bifocal lens surface sections can be i out after the'bifocal side of the blank has been ground. When it is desired to grind one of these bifocal lens sections to a prescription requiring considerable difierence between the curves on the bifocal side and the curve to be formed on the so-called prescription side, unless the original molded blank is made unusually thick, quite often there is not enough stock or glass material left in the blank to produce the curves desired, and if the molded blank is made thick enough to accommodate the curves for strong lenses, the amount of grinding is considerable.

This invention has for its main object a reduction in the amount of grinding required in finishing the prescription side of one piece bifocal lens blanks. In the manufacture, of bifocal lenses it is generall customary to use three or four base curves or the bifocal side of one piece'bifocal lenses. For 40 illustration, I have generally employed concave surfaces havin base curves of 4.50, 6.00 and 7.50 diopters. he practice is to use the 6.00 diopter base curve blank for lenses of low power. Therefore, if the convex side is of the blank is also molded plus 6.00 diopter curve, the amount of grinding necessary to produce the low power prescription lens is not very great. For stron convex lenses the 4.50 base curve blank 1s used and for strong concave lenses the 7.50 diopter base curve blank is used.

Now, if the convex side of these blanks is molded as is generally the custom, plus 4.50 diopters and plus 7.50 diopters respectively, 1t will be noted that considerable grinding will be required to make a strong convex lens on the 4.50 diopter base curve blank, inasmuch as the curve to be ground on the convex or prescription side would necessarily be much greater than 4.50 diopters and .the curve on the convex side of the 7.50 diopter base curve blank in the case of a strong concave lens would be considerably less than plus 7.50 diopters, and my invention has for its special object the production of a bifocal lens blank from which two bifocal lens sections can be cut, and having the prescription side of such sections so shaped as to materially reduce the grindin i'equired for producing the desired bifoca ens.

Other objects and advantages will appear from the following description taken in connection with the accompanying drawings, in which Figures 1. and 2am a top plan view of a bifocal lens blank of my invention.

Figure 3 is a section on line 3-3, Figure. 1.

Figure 4 is a section on line 4-4, Figure 2.

Figure 5 is a view of the bifocal side of a portion of the blank illustrating in dotted lines the place where the blank is split to produce two bifocal lens sections. 4

The blank of Figure 1 is designed particularly for the formation of two comparatively strong convex lenses, while the blank of Figure 2 is particularly designed for the formation of two comparatively strong concave lenses. As illustrated, the blank --1- is generally rectangular in form or outline having its opposite edges 2. and 3-- preferably substantially parallel while its opposite ends 4- and --5 are curved or arcuate in form.

The blank is of sufficient size so that when split upon the dotted line indicated in Figure 5, it is adapted for forming two bifocal lens sections from each of which a complete bifocal lens can be formed. The blank 1 has a concave surface 7- of continuous and uniform curvature throughout its entire surface. For illustration, this blank is preferably formed upon a 4.50 diopter base curve and upon this concave surface the bifocal lens surfaces are adapted to be ground preferably in the man ner shown by grinding the reading surface 8- at substantially the central portion of the blank -1, the distance surface being ground around it so that the distance surfaces of two bifocal lens sections are simultaneously formed and the reading surfaces of two bifocal lens sections are simultaneously formed, the blank being subsequently split to form two bifocal lens sections. The surface 9- of the blank --1 is shaped in a new and novel manner in that it is formed in two similar curved parts 10- .curve normal to the line -14.- with its center at 15 and the convex surface 11 has its curvature normal to the line 25 with its center at.-16. The two convex surfaces 10 and 11 are formed with curves of substantially the same radii and it will be obvious that the thickest portions of the two bifocal lens sections formed by splitting the blank, as indicated, will be at substantially the central portions of said sections so as to particularly adapt each section for desired formation with a minimum of grinding.

In Figures 2 and 4 the blank -1'7- has a concave surface 18 having, for

illustration, a base curve of 7.50 diopeters,

the entire surface being of substantially uniform curvature throughout and being substantially normal to the line -19 and with its center at 20. The opposite side of the blank -17 is formed with two similarly shaped curved surfaces 21- and 22 formed on a flatter curve, oi longer .radius than the concave surface 18. The surface 21'- is normal to the line 23- with its center of curvature at the point -24-- while the surface -22- is normal to the line -35 and has its center of curvature at the point 26. It will be noted in the construction of blank 17 that when it is split upon the line 6 indicated in Figure 5, two lens sections will be formed which are thinnest at their central portions, thereby peculiarly adapting them for the formation of a strong concave lens with a minimum of grinding.

It will be seen that broadly characterized, my invention comprises a bifocal lens blank which has a concave surface of uniform curvature throughout combined with two similarly curved surfaces upon the opposite" side of the blank, each of the latter surfaces having substantially the same radius of curvature but each differing in radius of curvature from the radius of curvature of the concave surface, and more specifically a blank which has a concave sur face on one radius, which surface constitutes one side of the blank, while the other side of the blank is formed with two convex surfaces of the same curvature, but

formed about different centers, and normal to different lines and having a different radius of curvature from that of the concave surface of the. blank.

Altho I have shown and described a particular shape of blank, the same being more or less rectangular, it will be obvious that my invention may be applied to various forms of blanks, and that changes may be made in the details of form. shape and particular arrangement of the parts, all within the scope of my invention, as set forth in the appended claims.

I claim:

1. A bifocal lens blank having a concave inner surface of substantially uniform curvature throughout, and an outer surface formed with two separate curved surfaces having substantially the same radius of curvature, but differing in radius of curvature from the concave inner surface of the blank.

2. A bifocal lens blank adapted to be split to form a plurality of substantially similar bifocal lens sections from each of which a complete bifocal lens can be formed, said blank having a concave surface with a continuous substantially uniform curvature throughout, and a convex surface upon the opposite side of the blank formed with a plurality of similar curved surfaces of different radius of curvature from the radius of curvature of the concave side of the blank. 1

3. A bifocal lens blank adapted to be split to form'a plurality of substantially similar bifocal lens sections from each of which a com lete bifocal lens can be formed, said blan having a concave surface with a continuous substantially uniform curvature throughout, a convex surface upon the opposite side of the blank formed with a plurality of similarly curved surfaces of substantially the same form and outline and having a different radius of curvature from the radius of curvature of the concave side of the blank.

a. A bifocal lens generally rectangular having a difierent radius of curvature from in form and having a concave surface with that of the concave surface of the blank. 10 a continuous substantially uniform curva- In witness whereof I have hereunto set ture throughout and the opposite surface of my hand this 2nd. day of April 1923.

the blank being formed with two curved HAROLD J. STEAD surfaces of substantiall the same radius of Witnesses:

curvature and arrange upon opposite sides MARY C. MURPHY,

of the longitudinalcenter of the blank and. W. R. Wm. 

